Transcoding a video is making a copy of a creative work. Ergo, by definition, copyright applies.
In fact, if transcoding a video added anything creative to the process, you would have two copyrights: one for the original creative work, and a second for the derivative (transcoded) work.
You missed it. OP has rights to the work. The question was whether downloading from Youtube breaks any laws. Youtube's add is transcoding, which is not a creative transformation. Ergo, OP probably has a legal right to download from Youtube, at least as far as copyright law is concerned.
No, I saw that. I was responding to the immediate parent, not the OP. The comment I was responding to was whether transcoding is an act covered by copyright, and it is.
The OP's comment was different. He was using youtube-dl to download videos uploaded by his own clients, which was fine because they're the copyright owners. Transcoding doesn't generally create a separate copyrighted work because at least for these types of media, the underlying representation of the bits doesn't matter.
Note: this isn't fair use. Fair use is a defense to violating copyright, and a copyright owner can't violate their own copyright ...but if they licensed one or more copyrights to a third party, they could violate the third party's copyrights depending on the terms of that license.
In fact, if transcoding a video added anything creative to the process, you would have two copyrights: one for the original creative work, and a second for the derivative (transcoded) work.